Aftermarket Knuckle Heads

This is not the sort of post that I enjoy writing.  I would much prefer to write a glowing report on a good product.  On the other hand, these things are not cheap, so I do believe it is reasonable to sound a warning so that buyers can make an informed purchase. 

Reproduction Knuckle heads from V-Twin Manufacturing.  The "issues" I will list range from minor annoyances to full blown problems.

First let's look at the annoying things.  The black paint on the heads is thin to the point of being translucent in many places, except of course in the areas that have runs.  As it turns out the runs are just as annoying as the see though if you opt to blast it off for a full refinish since the runs do a pretty good job of resisting removal with glass beads.

Speaking of paint, the heads were obviously painted before machining operations were performed, leaving large areas of bare cast iron.  Notably missing paint are the large spark plug "wells" and the tops of the rocker box supports.  Perhaps for this reason the machined surfaces were not deburred leaving sharp edges, many of them sharp enough to cut you quite easily when handing.  As it turns out, that can be VERY annoying.

The set I purchased was the version without rocker boxes and shafts, so they came without the upper rocker cover tins installed, but gaskets for them were included.  Upon inspection, they found a new home in a trash can, since they were so dried out and brittle that clearly  any attempt at installation would have been an exercise in futility.

The spring cups, or lower covers as they may also be called, have a nice Parkerized finish, and seem to be fairly good stampings (better than those from the same vendor a number of years earlier).  The brazed in oil return lines, however, have a copper plating which does not "take" the Parkerizing.  That may be a good thing in some ways, since the color may discourage some from trying to pass them off as originals.

On to what I consider a little beyond annoyances.  The valve spring are green.  So, what do you have against St. Patty's day, you might ask.  Well, green is not my favorite color, but this goes a little past interior decorating choices.  The valve springs are painted green.  In fact they are thickly painted green, possibly with a brush from the look.  Thick to the point of chipping off.  I can't say just what chunks of this green paint would do to an engine, or where it would ultimately wind up, but its certainly not something I would want to take a chance on.

The heads come with plumber style intake nipples installed.  In fact, they are installed with a "stock style" rivet to keep them from turning.  And when I say "stock style rivet" it is because the rivet is of the 1/4" diameter oversize normally reserved for a damaged hole on a used and abused head.  Too bad about that too.  Once the oversize rivets were removed, the nipples could be removed easily enough, meaning they were not installed very tight to begin with.  That added to the fact that the nipples had been installed with no type of sealer, leads one to conclude that the possibility of intake air leaks would be somewhere between likely and inevitable.

Next up is the alignment of the spring cups.  Keep in mind that these are held in place by being sandwiched between the valve guide and the head, so they need to be in the right position before the guide is installed all the way.  I keep a spare set of rocker boxes (knuckles) with shafts (no arms) among my special tools for just this purpose.  That way, I can insure that the spring cups align properly with the holes for the rocker shafts and that the other end of the cover fits into the hole in the rocker box.  In the case of this set of heads, not only did the rocker box end of the spring cups not line up with the knuckles, there was a good sized gap between the cup and ear on the head where the rocker shaft  passes through it.  Any attempts to correct this without driving the valve guides partially out would result in bending the lower spring cups, possibly with further damage.





Hard to tell form the poor photo, but this shows daylight between the spring cup and the rocker support ear on head



Going a little deeper yet, I found that the I.D. of the valve guides to be abnormally rough; not necessarily a good thing for longevity.  But, as it turns out, that would not be a problem after all, since the valve to guide clearance was too tight, meaning that by the time you honed the guides for more clearance, they would likely have a smooth interior.  Measuring the valve to guide clearance with a dial ball gauge showed .0022 to .003" on the intakes and .0034 to .0055 on the exhausts.  However, the fool proof final check for guides (at least in my book) is checking with a plug gauge (also known as a go/no go gauge).  This takes into account a valve guide bore that is not straight, something the ball gauge will not tell you.  In this case, a plug gauge .001" larger than the valve stem diameter would make it through one intake and and .002" larger on the other intake.  On the exhaust side a plug gauge .002 larger would go through one and .0025 larger on the other.  Stock clearances for a Knuckle are .004 to .006" clearance on both intake and exhaust.  I cannot imagine that these heads would have lived at these clearances.

The next item is only a problem if you plan to use these on a 61 inch motor.  The counter bore for the fire ring in the head is a slight interference fit on an OEM 61 inch Knuck cylinder.  That doesn't affect you if you have a 74 inch since there is no fire ring on the larger cylinder. 

The last item on my list does not really fit into either the annoyance or the problem column, and so possibly not worthy of mention, but I won't let that stop me.  Both exhaust valves had been treated to an approximate 45 degree cut on the combustion chamber side of the O.D.  I have seen the claim in print that this enhances flow.  It does not.  My guess is that this is an old wives tale started because someone saw a set of high performance ported heads with this modification and assumed it was for better flow.  In actuality, this extra angle is a last resort option for valve to valve clearance during overlap.  If one had a finished set of ported and flowed heads with less than the minimum required valve to valve at TDC, one might cut an angle on the margin of the exhaust valve only (because the resulting flow loss would less costly there).  Many years ago I tested this on my flow bench, and the result was so profoundly bad that it made an impression.  The margin thickness on a valve can have a large effect on its flow characteristics.

That pretty well wraps up this product review.  As I stated at the beginning, I wish I had better things to say about these heads, but there is this:  I think we can all be thankful that V-Twin put these heads into production.  The supply of repairable original Knuck castings is fast dwindling.  I believe they would be a better value if they were available as bare castings, but still, better something to work with than nothing at all.